Silicone impregnating materials are used for the preservation of buildings to reduce the water absorption of mineral building materials. Their high effectiveness is based, on the one hand, on the good spreading capability of the silicones on the free surface of the porous and capillary structure in the building material and, on the other, on the low surface tension of the silicones relative to water. Silicone impregnating materials are therefore used to hydrophobize facades as well as to chemically insulate horizontally against moisture rising in the capillaries of the walls. For both areas of application, the penetrating ability of the impregnating materials used is of decisive importance.
From the extensive patent literature, which relates to the impregnation of mineral building materials with organosilicon compounds, the following representative publications are named, which show different impregnating materials and/or methods for their production.
The European Pat. No. 0,015,366 relates to a method for the preparation of aqueous solutions of alkali organosiliconates, the organo part of which is an alkyl group with 1 to 3 carbon atoms, a vinyl group and/or a phenyl group, while the alkali part is a sodium or potassium ion. The method is characterized in that organopolysiloxanes of the general formula ##STR1## wherein R.sup.1 is alkyl with 1 to 3 carbon atoms, vinyl and/or phenyl,
R.sup.2 is alkyl with 1 to 4 carbon atoms, PA1 a is a number .ltoreq.2 and PA1 x is 1 to 1.25, PA1 R.sup.2 represents a monovalent hydrocarbon group with 1 to 18 carbon atoms, PA1 x has a value of 0.75 to 1.5 and PA1 y has a value of 0.2 to 2.0, and PA1 R.sup.2 is methyl or ethyl, PA1 a=0 to 1.5, PA1 b=1.0 to 4.0 and PA1 a+b=2.0 to 4.0, PA1 1. As alkoxysilanes and/or alkoxysiloxanes, the methoxy and ethoxy compounds are selected. The ethoxysilanes and/or ethoxysiloxanes, the hydrolysis of which releases physiologically safe ethanol, are preferred. When methoxy compounds are used, the fact that methanol is split off must be taken into account. However, all the other advantages of the inventive method apply also for the methoxy compounds. PA1 2. Deviating from the state of the art, the aqueous solutions of the hydrolysates are produced continuously. As a result, the impregnating solution is prepared at the same rate at which it is used. This ensures that the solutions for impregnating building materials are available in a constant quality and that thus an impregnation of constant quality is achieved. More particularly, it is avoided that solutions of different degrees of ageing are used. A quality control of the solutions by the operating personnel, which in any event is difficult to carry out, becomes superfluous. PA1 3. The solutions, obtained in a continuous operation, are applied on the mineral building material within the space of 3 to 30 minutes after the alkoxysilanes and/or alkoxysiloxanes are mixed with water.
are reacted with aqueous solutions of NaOH or KOH having a concentration of 0.7 to 0.9 moles/100 g at temperatures .gtoreq.80.degree. C., the liberated alcohol R.sup.2 OH is distilled off, if necessary, and/or the solution of the reaction product is adjusted to the desired concentration with water.
In this method, in which a filtration step is avoided, alkali chloride-free alkali organosiliconate solutions are obtained, with which mineral materials can be impregnated.
The German Offenlegungsschrift 2,330,887 is directed to the use of alkyl/aryl-alkoxypolysiloxanes of the general formula ##STR2## wherein R.sup.1 is alkyl with 1 to 4 carbon atoms, R.sup.2 is phenyl and/or methyl, a=0.5 to 1.7, b=0.06 to 2.5 and 4-(a+b).gtoreq.1, for impregnating inorganic materials, as well as coal, especially during briquetting.
These compounds are used especially in the form of their solutions in organic solvents such as benzene, toluene or normal commercial aromatic distillates or solvents based on esters or ketones or in the form of aqueous emulsions.
The German Offenlegungsschrift 3,323,908 discloses aqueous emulsions of low molecular weight, alkoxy-functional silicone resins, which have a long shelf life and contain
(a) 1-60% by weight of silicone resin of the general formula ##STR3## wherein R.sup.1 represents a monovalent hydrocarbon group with 1 to 14 carbon atoms
and having a viscosity of 2 to 2,000 mPa.times.sec,
(b) 0.1 to 10% by weight of an emulsifying agent and
(c) water.
The emulsions are used for hydrophobizing mineral materials, the emulsions being said to have a good stability.
In the German Offenlegungsschrift 3,037,220, aqueous solutions of hydrolyzed alkyltrialkoxysilanes, especially propyltrialkoxysilanes, are described, in which the alkoxy group has 1 to 4 carbon atoms. These solutions are said to be relatively stable and to remain clear for several hours, depending on the degree of acidity.
However, these known materials for impregnating mineral building materials show a series of disadvantages, so that a satisfactory solution to the problems of impregnating mineral building materials is not yet known. Essentially the following disadvantages may be observed.
It is true that aqueous solutions of alkali organosiliconates have the required penetrability for mineral building materials; however, curing of the alkali siliconates takes place in the presence of CO.sub.2 with formation of alkali carbonate. This curing reaction proceeds slowly and incompletely. The hydrophobizing efect is therefore not very good. Particularly disturbing is the formation of water-soluble salts, which remain in the building material and, under certain conditions, may lead to white coatings on the dry building material surface. Moreover, alkali carbonates may cause salt damage, the building material surface thus occasionally breaking off.
If solutions of low molecular weight silicone resin intermediates or precursors in the aforementioned solvents are used, a high penetration by the solutions into the building materials is admittedly achieved, although at the expense of disadvantages, which occur with the use of an organic solvents. Thus, the odor, flammability and/or the physiological dubiousness of organic solvents are particularly disturbing. These disadvantages are particularly important, when the hydrophobizing of masonry is effected to restore old buildings. The necessary precautionary measures, which must be adhered to when working with organic solvents, moreover keep many potential users from employing such products.
If mineral building materials are impregnated with aqueous emulsions of low molecular weight alkylalkoxysiloxanes, only relatively slight penetration values are achieved. The relatively large droplets of the disperse phase block and clog the pores of the masonry and prevent penetration by the emulsion into the depth of the masonry. The deposition or separation of the siloxane at or near the surface of the building material is, moreover, favored by the fact that the masonry absorbs the continuous phase of the emulsion, so that the emulsion breaks relatively quickly. As a result, the organosilicon phase once again preferentially collects in the region of the surface.
Other difficulties and disadvantages arise if one starts out from alkylalkoxysilanes and at the place where they are to be used, hydrolyzes these in water to the corresponding silanols. This is so, because the silanols, formed in the aqueous solution by the hydrolysis, condense to siloxanols under the conditions of the hydrolysis, for example, at a pH ranging from 3 to 5, low molecular weight, water-soluble siloxanols being formed first. However, the latter condense further with an increase in the size of the molecules if the solution is permitted to stand. The solutions finally become cloudy and, depending on the length of storage, more highly condensed products precipitate from the solutions. From an applications point of view, this is particularly disadvantageous, because one of the factors, on which the hydrophobizing effect depends, is the molecular weight of the hydrolysis products. As a result, the hydrophobizing action of the solution decreases continuously, especially in the case of building materials that are difficult to penetrate, such as clinker, concrete and natural stone with a small pore volume. This deterioration sets in already when the solution is still clear. It is therefore not possible for the user at the construction site to employ an impregnating solution, which always has the same effectiveness. Usually solutions are used on the spot in the amount in which presumably they will be required. The impregnating treatment commences on formation of the clear solution and extends over a period of several hours. Since the condensation reaction proceeds during this period, the hydrophobizing effects deteriorate gradually. As a result, the hydrophobized areas are inhomogeneously hydrophobized, which becomes apparent because of the different extent of the water repellancy. At the same time, it should be taken into consideration that the extent of expertise of the workers involved in the impregnating is generally limited. It is therefore also entirely possible that solutions, which are already slightly cloudy, will be used, since this cloudiness cannot always be recognized in the containers at the building site.
The rate of hydrolysis of the alkoxysilanes and of the low molecular weight alkoxysiloxanes depends on the molecular weight and especially on the nature of the alkoxy groups. If methoxysilanes are used, relatively mild conditions are sufficient to achieve an adequate hydrolysis rate or speed. Under such conditions, the condensation of the silanol/siloxanol mixtures proceeds relatively slowly. However, the release of methanol during the reaction is a disadvantage. If alkoxysilanes or low molecular weight alkoxysiloxanes with ethoxy, propoxy or alkoxy groups with even longer chains are used, the hydrolysis takes longer or the reaction must be catalyzed more strongly. This, however, also leads to an acceleration of the condensation rate. The time span between obtaining a usable, clear, aqueous solution of the silanol/siloxanol mixtures and a no longer usable solution with more highly condensed products becomes small. The usability of the solution on particularly fine-pored building materials may therefore deteriorate already after 30 to 60 minutes.